ARTHROPODS AND MOLLUSCS 179 



to create a cloud in the water and thus escape unperceived, 

 The squids commonly used as bait by fishermen also belong 

 to the decapods. 



The octopods have a short sac-like body and neither an 

 external nor internal shell. To this group belong the famous 

 devil-fishes (octopus) whose strange and terrifying appear- 

 ance combined with their frequently great size, has furnished 

 the basis for many a weird tale of the sea. Devil-fishes hav- 

 ing tentacles more than thirty feet in length have been 

 found. 



The pearly nautilus is a cephalopod of four gills instead of 

 two as with the octopods and decapods, and is the only 

 existing member of what was in the early times of earth's 

 history a large group of animals. They make a many- 

 chambered, spiral shell with its inner surface lined with 

 beautiful pearly nacre. 



